Question

When I have to write methods which return two values, I usually go about it as in the following code which returns a List<string>. Or if I have to return e.g. a id and string, then I return a List<object> and then pick them out with index number and recast the values.

This recasting and referencing by index seems inelegant so I want to develop a new habit for methods that return two values. What is the best pattern for this?

using System;
using System.Collections.Generic;
using System.Linq;

namespace MultipleReturns
{
    class Program
    {
        static void Main(string[] args)
        {
            string extension = "txt";

            {
                List<string> entries = GetIdCodeAndFileName("first.txt", extension);
                Console.WriteLine("{0}, {1}", entries[0], entries[1]);
            }

            {
                List<string> entries = GetIdCodeAndFileName("first", extension);
                Console.WriteLine("{0}, {1}", entries[0], entries[1]);
            }

            Console.ReadLine();
        }

        /// <summary>
        /// gets "first.txt", "txt" and returns "first", "first.txt"
        /// gets "first", "txt" and returns "first", "first.txt"
        /// it is assumed that extensions will always match
        /// </summary>
        /// <param name="line"></param>
        public static List<string> GetIdCodeAndFileName(string line, string extension)
        {
            if (line.Contains("."))
            {
                List<string> parts = line.BreakIntoParts(".");
                List<string> returnItems = new List<string>();
                returnItems.Add(parts[0]);
                returnItems.Add(line);
                return returnItems;
            }
            else
            {
                List<string> returnItems = new List<string>();
                returnItems.Add(line);
                returnItems.Add(line + "." + extension);
                return returnItems;
            }
        }

    }

    public static class StringHelpers
    {
        public static List<string> BreakIntoParts(this string line, string separator)
        {
            if (String.IsNullOrEmpty(line))
                return null;
            else
            {
                return line.Split(new string[] { separator }, StringSplitOptions.None).Select(p => p.Trim()).ToList();
            }
        }
    }
}

Added:

Ok, thanks everyone, I like the “return a custom class” answers best, never really thought out was that easy to read, seems like a hack to me returning the first variable one way and the second another, here is my refactoring returning a custom class:

using System;
using System.Collections.Generic;
using System.Linq;

namespace MultipleReturns
{
    class Program
    {
        static void Main(string[] args)
        {
            string extension = "txt";

            {
                IdCodeFileNamePair pair = GetIdCodeAndFileName("first.txt", extension);
                Console.WriteLine("{0}, {1}", pair.IdCode, pair.FileName);
            }

            {
                IdCodeFileNamePair pair = GetIdCodeAndFileName("first", extension);
                Console.WriteLine("{0}, {1}", pair.IdCode, pair.FileName);
            }

            Console.ReadLine();
        }

        /// <summary>
        /// gets "first.txt", "txt" and returns "first", "first.txt"
        /// gets "first", "txt" and returns "first", "first.txt"
        /// it is assumed that extensions will always match
        /// </summary>
        /// <param name="line"></param>
        public static IdCodeFileNamePair GetIdCodeAndFileName(string line, string extension)
        {
            if (line.Contains("."))
            {
                List<string> parts = line.BreakIntoParts(".");
                List<string> returnItems = new List<string>();
                return new IdCodeFileNamePair { IdCode = parts[0], FileName = line };
            }
            else
            {
                List<string> returnItems = new List<string>();
                return new IdCodeFileNamePair { IdCode = line, FileName = line + "." + extension };
            }
        }

    }

    public static class StringHelpers
    {
        public static List<string> BreakIntoParts(this string line, string separator)
        {
            if (String.IsNullOrEmpty(line))
                return null;
            else
            {
                return line.Split(new string[] { separator }, StringSplitOptions.None).Select(p => p.Trim()).ToList();
            }
        }
    }

    public class IdCodeFileNamePair
    {
        public string IdCode { get; set; }
        public string FileName { get; set; }
    }
}

Answer 1

I prefer either to create a lightweight class with two properties (see below), or to use a tuple (now available baked into the framework in .NET 4 but not hard to write your own)

class MyReturnValue
{
    public string Id { get; set; }
    public string Name { get; set; }
}